Energy absorbing bumper system

ABSTRACT

An energy absorbing bumper system for automotive vehicles includes a pair of fluid-filled telescopic cylinder units at respective ends of the bumper mounting the same to the vehicle chassis. Variable volume fluid chambers within each unit have the fluid flow therebetween controlled by a floating orifice and metering rod and one of the chambers is bounded by a gas piston urged by a body of compressed gas to force the telescopic mounting unit to a definite extended or normal position wherein the cylinders of the unit are snugly interengaged to resist relative radial displacement in rough road conditions and the like.

United States Patent Jackson et al.

ENERGY ABSORBING BUMPER SYSTEM Inventors: George W. Jackson; Paul J.Long, Jr.; Wayne V. Fannin, all of Dayton, Ohio General Motors Detroit,Mich.

Filed: Nov. 19, 1970 Appl. No.: 91,008

Assignee: Corporation,

US. Cl. ..293/70, 293/89, 267/ 139,

Int. Cl. ..B60r 19/02, Fl6f 9/06 Field of Search ..293/1, 9, 24, 60, 70,73, 85, 293/86, 89, DIG. 2; 267/64 R, 116, 139, 140; 213/43, 223

References Cited UNITED STATES PATENTS 2,348,160 5/1944 Thomhill..267/64 R 2,618,478 11/1952 Conway ..267/64 R 2,167,928 8/1939 Johnson..267/64 R 3,008,746 11/1961 Senger ..293/70 Primary Examiner-Gerald M.Forlenza Assistant Examiner-Robert Saifer Attorney-W. E. Finken and D.L. Ellis [57] ABSTRACT An energy absorbing bumper system for automotivevehicles includes a pair of fluid-filled telescopic cylinder units atrespective ends of the bumper mounting the same to the vehicle chassis.Variable volume fluid chambers within each unit have the fluid flowtherebetween controlled by a floating orifice and metering rod and oneof the chambers is bounded by a gas piston urged by a body of compressedgas to force the telescopic mounting unit to a definite extended ornormal position wherein the cylinders of the unit are snuglyinterengaged to resist relative radial displacement in rough roadconditions and the like.

5 Claims, 4 Drawing Figures i lllll Patented Oct. 24, 19 72 INVENTO RSGeorge [1/ Ix/6012, 9, J1: 5

Pall/1K0): BYl/ayzze 1.

5 Afiz ATTORNEY ENERGY ABSORBING BUMPER SYSTEM This invention relates toenergy absorbing bumper assemblies for automotive vehicles and moreparticularly to improved hydraulic type energy dissipating chassismounting units for automotive bumpers.

In the application of energy absorbing devices or units of the hydraulictype to the impact bumper assemblies of automotive vehicles, paramountconcerns in the durability and performance of such units are thesomewhat conflicting needs for relatively free sliding movement betweentelescopic portions of the unit, even under loading applied atsubstantial angles to the axis of the unit, the prevention of anysubstantial leakage of fluid in the units in extended service, and therequirement of rigidity in those parts of the unit relied upon tosuspend or mount the bumper on the vehicle.

On the concern for proper sliding performance even under forces angularto the unit axis in their energy absorbing excursions, thetelescopically related members of the unit should not bind on or deformone another and should readily accommodate the severe forces andnonuniform displacement that arise between the two ends of the bumper asoccurs during cornering impacts on only one side of the bumper. Yet, thedesign of the units must be such that in their normal extended conditionthey are sufficiently rigid to withstand the impulses and vibration ofrough road operation and the forces applied to the bumper bar duringjacking or towing of the vehicle.

The primary feature of this invention is that it provides an improvedhydraulic type energy absorbing unit for automotive vehicle bumpersystems adapted to accomplish these objectives. A specific feature ofthis invention is the arrangement within such an hydraulic energyabsorbing bumper mounting unit of telescopically arranged membersproperly sized and fitted with bearings for relatively free slidingduring variously angularly applied impact loadings on the bumper bar butwhich include stabilizing means for snugly interengaging these membersin a normal extended position through utilization of tapering surfacesadapting the cylinders to withstand severe rough road shake and jackingand towing forces. Yet more specifically, the invention featuresspecially selected frusto-conical surfaces, in the case of cylindermembers, interengageable under the force of bumper restoring biasingmeans within the unit in the form of a body of compressed gas or thelike urging the unit to a maximum extended position which is defined bythe relative location of the interengaging surfaces on the cylinders.

Further in the interest of accommodating whatever limited beaming orlike deflection that may occur in the unit during free sliding energyabsorbing excursions and additionally in the interests of accommodatinglimited manufacturing variations, the invention features the use of atapered or varying cross section metering pin and orifice combinationwherein the pin is rigidly affixed to one of the telescoping members andthe piston associated with the other member carries a floating annularorifice member radially slidable to accept whatever misalignment thatmay occur between the metering rod and the piston.

These and other features and advantages of the invention will be readilyapparent from the following specification and from the drawings wherein:

FIG. 1 is a perspective view of an automotive vehicle chassis frameincluding an energy absorbing bumper assembly according to thisinvention;

FIG. 2 is an enlarged sectional view taken generally along the planeindicated by lines 2-2 of FIG. 1 showing the bumper bar in its normalextended position;

FIG. 3 is a sectional view taken generally along the plane indicated bylines 3-3 of FIG. 2; and

FIG. 4 is a view similar to FIG. 2 showing a modification of theinvention.

Referring now particularly to FIG. 1 of the drawings, reference numeral10 generally designates a separate chassis frame of an automotivevehicle which typically includes a laterally spaced pair oflongitudinally extending side rails 12 interconnected in the forwardportions of the frame by a front cross member 14. It will be understoodthat rather than the separate chassis frame illustrated herein, theautomotive bumper applications of this invention are equally welladapted to be employed in unibody construction.

The bumper assembly includes a generally conventional impact bumper orface bar 16 which, as seen best in FIG. 2, includes'an inner reinforcingplate 18. Energy absorbing chassis mount units, each designatedgenerally as 20, are provided adjacent each end of bumper bar 16 forrigid attachment between reinforcing plate 18 and forward horns 22 ofthe side rails 12.

Referring to FIGS. 1 and 2, each mounting unit 20 includes an outercylinder 24 of a selected stock thickness suitable to the contemplatedimpact fluid pressure and normal bumper mount loadings to beencountered. Adjacent its outer or forward end, each cylinder 24 haswelded thereto a surrounding bracket 26 extended with an annular portionembracing the cylinder and a flange provided with bolt holes, while atits inner or rearward end, the cylinder is closed by a cap 28 which mayhave welded or otherwise rigidly affixed centrally thereto a threadedstud 30. On each frame horn 22, a spaced pair of L-shaped brackets arerigidly attached, the forward one 32 of which includes an aperture forreceiving cylinder 24 and has bracket 26 secured thereto by bolts 36while the rearward one of which 34 may receive the stud 30 which isthreaded over with a nut thereby to rigidly mount the cylinder 24 on theframe horn at these suitably longitudinally spaced locations of thebrackets.

The mounting unit 20 further includes an inner or second cylinder member38 also of properly chosen stock thickness and telescopically receivedwithin cylinder 24 and extending forwardly therefrom, with a weld plate40 being provided at its outer terminal end. Welded to plate 40 is asleeve 42 extending vertically and receiving a rubber or similar elasticbushing 44 bonded or otherwise attached intermediate the sleeve and aninner mounting bar 46 which is provided with flattened ends aperturedfor the reception of mounting bolts. A generally U-shaped mounting strap48 is welded or otherwise afiixed at the proper laterally spacedlocations on the bumper bar reinforcing plate 18 to directly engage theouter sides of respective sleeves 42, bent ears of each strap beingapertured to receive bolts 50 extending through the mounting bar 46 andthreaded over with nuts to secure the bumper l6 and cylinders 38together.

At the inner or rearward end of each cylinder 38, a wall member in theform of a cylinder cap 52 generally delineates opposite fluid chambersin the mounting unit 20 each filled with a suitable fluid such as oil. Aliner or bearing sleeve 54 of glass-filled nylon or other plasticmaterial exhibiting suitable antifriction, antiscoring and loaddeformation and stiffness properties is received over the cylinder cap,these properties being chosen to best accommodate the required freesliding movement in unit 20 as well as the large radial forces seen bythe bearing under impact and under jacking and towing forces applied tobumper bar 16. Sufficient free sliding movement is permitted between thecylinder 24 and the sleeve 54 by provision of adequate clearance. Forexample, with the inner diameter of cylinder 24 approximating 2.5inches, an outer diame ter for sleeve 54 providing a total ordiametrical clearance of about0.0l inch is preferred. By the use of suchclearance or additionally by shallow grooves provided in the sleeve, notshown, sufficient fluid communication is provided between the remoteside of the cylinder cap 52 and the exterior of inner cylinder 38 in acylinder interspace 56, so that the right hand fluid working chamber ofunit 20 is comprised of the volume rightwardly of cylinder cap 52 aswell as this interspace 56.

Within inner cylinder 38, a piston 58 fabricated of sheet metal or thelike is slidably received and fitted with an O-ring 60 to adequatelysealingly bound or define one side of the working fluid chamber withincylinder 38 leftward of the cylinder cap 52, as shown in the drawings. Aquantity of gas is compressed within the volume between piston 58 andplate 40, such gas being injected through plate 40 by conventionaltechniques during unit assembly and using as a closure a ball 62 weldedwithin the gas filling orifice in plate 40 following the gas insertion.In the typical unit 20 such as described, the inside diameter ofcylinder 24 provides for an effective piston area operative on cylinder38 of approximately square inches. This, taken with initial compressionof the gas, which may for example be nitrogen, of approximately 150p.s.i. when the parts are in the normal extended position shown in FIG.2, yields a force of approximately 750 pounds fromthe gas-compressedfluid urging the inner cylinder 38 in an outward direction to the normalextended position.

An orifice element 64 is received within an aperture 66 in the cylindercap 52. Element 64 is sharp-edged at 68 and generally U-shaped inlongitudinal section to include radial flanges which embrace the pistoncap. The orifice element 64 is seen as being sized with some limitedclearance, chosen for a purpose to be described, between its annularwall intermediate the flanges and aperture 66 so that the element mayfloat or radially slide within the aperture.

A metering rod 70 has one end welded centrally of the cap 28 and extendsforwardly to be received within the orifice element 64. The rod 70 is ofbasically cylindrical form and has milled or otherwise formed thereinthree equally spaced flats or plane surfaces 72 disposed commonly atvarious angles to the rod centerline over the length of the latter toexhibit varying depth relative to the gross or cylindrical dimension ofthe rod. As seen best in FIG. 3, the cylindrical dimension of the rod issized closely to the diameter of orifice element 64 at sharp-edge 68 sothat the element seats or is guided by the unflatted portions of therod. Hence, during an energy absorbing excursion under impact forcestelescoping cylinder 38 and piston cap 52 inwardly, any slight axialmisalignment between the metering rod and aperture 66 is accommodated bythe predetermined limited amount of radial floating or sliding movementof orifice element 64 permitted by its radial clearance from the edge ofaperture 66. Rather than this floating orifice, it may be preferable tofix the orifice on the piston cap and mount the inner end of themetering ro movably on the cap 28, as by a swivel.

In an energy absorbing operation or excursion of units 20, and takingfor example the energy of a strictly longitudinal impact force appliedcentrally of bumper bar 16, each unit 20 is adapted to experience anaxial inward telescoping of cylinder 38 from the normal extendedposition shown, permitting rearward displacement of the bumper barevenly along its length. Where the impact forces are sufficient toovercome the initial precornpression of the gas spring behind piston 58,any such inward telescoping of the cylinders must of course beaccompanied by displacement of fluid from the right hand workingchambers in cylinders 24 through the orifice 64 and into the leftwardworking chambers within cylinders 38. As is known in the art, themetering rod may be formed, such as by flats 72, to provide a graduallydecreasing amount of orifice area between the rod and sharp-edge 68 fora gradually correspondingly increasing fluid resistance to inward motionof cylinder 38, thus to maintain a substantially constant pressurizationof the right hand chamber as the velocity of unit displacement graduallydecreases. This results in a generally so-called square force vs.displacement characteristic curve and in terms of such curve the productof the pressure force on the effective piston area on cylinder 38 overunit displacement times such displacement will represent the requiredamount of energy of impact to be absorbed'by passage of metered fluid.Typically, the two units 20 will be designed to each carry a maximumpressurization force related to the strength of the regions of frame 10to which they are attached, these maximum forces of course representinga corresponding relative velocity of impact with which a vehicle ofgiven mass will strike, for example, a fixed solid barrier. Theconformation of flats 72 may accordingly be tailored to this maximumcontemplated impact velocity, and where lesser velocity impacts areimposed on units 20, lesser pressurization forces will develop thereinbut the entire kinetic energy thereof will nevertheless be absorbed.

Other than square characteristic curve performance may be desired inunits 20 and, this is again easily controlled by the angleor depth ofthe flats 72 along the length of rod 70. In one preferred design of unit20, the flats 72 are of constant depth over about the first one-fifth ofrod length whereupon they become increasingly shallower forprogressively decreasing orifice area. In this way, a purposely lowinitial pressure force level resulting from low fluid restrictioncompensates for additional structural internal loads or resistances tounit displacement that may occur in a limited initial period or strokeof impact and arising from inertia of the moving parts or friction.Following cessation of these brief additional resistances,

uniformly varying depth portions of flats 72 contribute the primary andcontrolled resistance to unit displacement in the manner describedabove.

Following the absorption of the impact energy and the inwarddisplacement of the cylinders 38, a greater portion of fluid iscontained in the leftward working chambers in such cylinders therebyhaving forced pistons 58 leftwardly to additionally compress the gasspring behind these pistons. Potential energy imparted through thiscompression acts upon the release of the impact forces on the bumper barto expand the gas spring chamber and forcibly displace the cylinders 38and bumper bar 16 leftwardly back to the original normal extendedposition shown in the drawings. The working fluid is thereby forced fromthe leftward chambers through orifice 64 so that the units are permittedto assume their original volume, readied for repeated impacts.

As indicated hereinabove, the initial precharge of the gas behindpistons 58 is chosen to be sufficiently large to provide on thecylinders 38, even in their normal extended position shown, a forceseeking to move the same further outwardly. In the interests of assuringa very rigid interconnection between each cylinder 38 and its matingcylinder 24, combined bearing and stabilizing means are provided thereonwhich utilize this outward thrust and in a form which includes a pair oftapering or wedge surfaces engageable in the normal extended position ofthe units 20. As seen best in FIG. 2, the terminal end portion 73 ofcylinder 24 is provided with an inward taper by deforming the same tothe desired angle following initial assembly of the cylinders inmanufacture. Cylinder 38 has welded or otherwise affixed thereto at aselected location an annular bearing and stabilizing member or ring 74having at its outer extremity a similar tapering surface 76. In the caseof cylindrical forms for units 20 such as shown in the drawings, theseare frusto-conical surfaces best formed with an angle to the unitcenterline of not less than about so that no tendency toward amechanical locking taper results. Under the bias of the gas springbehind pistons 58 forcing cylinders 38 leftwardly, the surface 76 ofstabilizing ring 74 engages snugly with the inner wall 78 of the taperedend portion 73 of cylinder 24 for rigid abutment therebetween preventingradial play or looseness in units and the shake or vibration of bumperbar 16 which would otherwise result. The largest diameter of stabilizingring 74, which provides the bearing area between the cylinders duringdisplacement, and in keeping with the similar clearance at piston sleeve54, is chosen sufficiently smaller than the inner diameter of cylinder24 so that, following disengagement of the frusto-conical surfaces in anenergy absorbing excursion, sliding movement between the cylinders islargely unimpeded. However, following the impact stroke, the forcedreturn of the cylinders 38 again snugly interengages surfaces 76 and 78for the required lateral rigidity. This largest diameter or bearing areaof the stabilizing ring 74 may actually be constituted by a suitableglass-filled nylon or other plastic sleeve having properties similar tothat of sleeve 54. This may take the form, as shown, of a plastic ring80 seated in a groove in the stabilizing member and overlapped at itsinward edge generally to fill the interspace 56 over a limited length.Such ring may be provided with a concave surface for nesting of asealing O-ring 82 which prevents leakage of fluid past the stabilizingring to the exterior of cylinder 24. With respect to interspace 56, suchO-ring and stabilizing ring 74 behind it define an annular piston facecomplementing cylinder cap 52. If desired, the material and size of ringmay be specially chosen to also act as a seal, especially were itextended to overlap the taper surfaces so as to be compressed under thereturn force of the gas spring.

By locating the inner tapered wall 78 on the terminal end portion 73 ofcylinder 24, the principal lateral load bearing region defined bysurfaces 76 and 78 is located as close as possible to the mass load ofbumper 16 and internal beaming deflection of cylinder 38 is minimized oreliminated. Since the tapers of surfaces 76 and 78 center the cylinder38 relative to cylinder 24, O-ring seal 82 is advantageously locatedimmediately adjacent thesesurfaces so that it will adequately seal theentire annular space 56 with substantially uniform force and compressionabout its periphery and thereby avoid localized compression set ortearing and scoring. Also, with the O-ring permitted to be thus located,annular space 56 may be filled with fluid with the unit extended and noopen volume susceptible to accumulation of dirt, etc., is presentedwhich might result in abrasion or other harmful effects on the outerbearing, which is here provided by stop ring 74 and ring 80, duringrepeated stroking of the unit. In a modification shown in FIG. 4, thering 80 on stabilizing member 74 and the sleeve 54 are eliminated infavor of gaining the stronger deformation resistance of metal materialin the stabilizing ring and cylinder cap 74 and 52' respectively. Tominimize wall scoring or abrasion during impact excursions, thesebearing members or rings may be fabricated of brass, aluminum or thelike. An additional packing ring 84 is provided against the stabilizingring 74'. It is to be observed that in both embodiments, substantialdistance separates these bearing members longitudinally of cylinder 38so that, taken with the bending strength of the latter, strong supportis provided for heavy bumper bars 16.

While the above description deals with a purely longitudinally centrallyapplied impact load on bumper bar 16, it will be appreciated that byvirtue of the sleeve and bushing mounting arrangement at the forwardends of cylinders 38, the bumper assembly employing these units 20 iscapable of receiving cornering impacts which substantially deflect onlyone end of the bumper bar and only one of the bumper units 20. In theseinstances, pivoting movement or relative rotation between the mountingbars 46 and the sleeves 42 is accommodated by bushing 44 during therelative rotation of the bumper bar on the frame 10.

Having thus described the invention, what is claimed 1. An energyabsorbing mounting unit for impact bumper bars of automotive vehiclescomprising inner and outer tubular members the inner of which is adaptedfor attachment to a said bar and the outer of which is adapted forattachment to the vehicle structural frame, said inner member beingslidably received within said outer member with an annular clearancespace between the walls thereof and for telescoping movement between aselected extended relationship and any of a plurality of telescopedrelationships, bearing means between said members permitting relativelyfree telescoping movement of said membersunder impacts applied to saidbumper bar and including a first bearing element located adjacent theterminal open end portion of said outer member and a second bearingelement spaced from said first element within said outer memberlongitudinally a distance substantially equaling the length of saidinner member enclosed by said outer member in said extended relationshipof said members, said second bearing element defining fluid passagemeans permitting communication of fluid either side thereof, axiallyaligning load supporting taper surfaces on said members including afirst generally taper surface on said terminal end portion of said outermember and a complementary taper surface on said inner member engageablein the extended relationship of said members, an annular sealing memberdisposed on said inner member immediately closely adjacent therespective said taper surface thereon and thereby uniformly sealinglyengageable about its periphery between said members in an axiallyaligned relation with said taper surfaces engaged in the extendedrelationship of said members, and a quantity of fluid sealedly containedwithin said inner and outer members by said sealing member includingwithin the annular volume of said annular clearance space definedbetween said second bearing element and said sealing member with theparts in the extended relationship thereof.

2. An energy absorbing mounting unit for impact bumper bars ofautomotive vehicles comprising, inner and outer tubular members theinner of which is adapted for attachment to said bar and the outer ofwhich is adapted for attachment to the vehicle structural frame, saidinner member being slidably received within said outer member with anannular clearance space between the walls thereof and for telescopingmovement between a selected extended relationship and any of a pluralityof telescoped relationships, bearing means between said memberspermitting relatively free telescoping movement of said members underimpacts applied to said bumper bar and including a first bearing elementmounted on said inner member at a location engageable with the terminalend portion of said outer member with the members in extended relationand a second bearing element mounted on said inner member at a locationspaced from said first element longitudinally a distance substantiallyequaling the length of said inner member enclosed by said outer memberin said extended relationship of said members, said second bearingelement defining fluid passage means permitting communication of fluideither side thereof, stabilizing means on said members including a firstgenerally frusto-conical crimp surface at the margin of said outerterminal end portion of said outer member'and a complementaryfrusto-conical surface on said inner member engageable in the extendedrelationship of said members to axially align said members and providefirm lateral load bearing support between said members in said extendedrelationship thereof, an annular sealing member disposed on said innermember immediately closely adjacent said complementary frusto-conicalsurface and thereby uniformly sealingly engageable about its peripherybetween said members in a centered relation in the extended relationshipof said members, and a quantity of fluid contained within said inner andouter members including within the annular volume of said annularclearance space defined between said second bearing element and saidsealing member with the parts in the extended relationship thereof.

3. An energy absorbing mounting unit for impact bumper bars ofautomotive vehicles comprising, inner and outer tubular members, one ofsaid members being adapted for attachment to the vehicle and the otherthereof for attachment to 'a bumper bar, said inner member beingrelatively freely slidably received within said outer member forrelative telescoping motion under impact forces applied to the bumperbar from a normal extended relationship to any of a plurality oftelescoped relationships, means biasing said members to said normalextended relationship thereof, means defining a pair of variable volumefluid chambers within said members, fluid within said chambers, ametering rod rigidly afifixed to one of said members, a piston wall onthe other of said members and an aperture in said piston wallcommunicating said chambers and having projecting therethrough an endportion of said rod, and an annular orifice member including an annularwall mounted within said aperture of said piston wall to extend in adirection axially of said members past both sides of said piston walland sized for limited radial shifting movement within said aperture,said annular wall receiving said end portion of said rod, said orificemember further including a pair of radially extending flanges integralwith said annular wall and embracing said piston wall with clearancewhereby said orifice member is retained on said piston wall yet isradially shiftable to accommodate axial misalignment between said rodand said aperture during telescoping movement of said members betweensaid normal extended relationship and a maximum telescoped relationship.

4. The mounting unit recited in claim 3 wherein said metering rod isshaped generally cylindrical along its length and includes at least onevarying depth flat thereon interrupting the cylindricity thereof, thecylindrical contour of said metering rod being engaged with acylindrical inner surface of said orifice member annular wall forguiding the latter radially in said aperture.

5. An energy absorbing mounting unit for impact bumper bars ofautomotive vehicles comprising, inner and outer tubular members theinner of which is adapted for attachment to said bar and the outer ofwhich is adapted for attachment to the vehicle structural frame, saidinner member being slidably received within said outer member with anannular clearance space between the walls thereof and for telescopingmovement between a selected extended relationship and any of a pluralityof telescoped relationships, bearing means between said memberspermitting relatively free telescoping movement of said members underimpacts applied to said bumper bar and including a first bearing elementmounted on said inner member at a location engageable with the terminalend portion of said outer member with the members in extended relationand a second bearing element mounted on said inner member at a locationspaced from said first element longitudinally a distance substantiallyequaling the length of said inner member enclosed by said outer memberin said extended relationship of said members, said second bearingelement defining fluid passage means permitting communication of fluideither side thereof, stabilizing means on said members including a firstgenerally frusto-conical crimp surface at the margin of said outerterminal end portion of said outer member and complementaryfrusto-conical surface on said inner member engageable in the extendedrelationship of said members to axially align said members and providefirm lateral load bearing support between said members in said extendedrelationship thereof, an annular sealing member disposed on said innermember immediately closely adjacent said complementary frusto-conicalsurface and thereby uniformly sealingly engageable about its peripherybetween said members in a centered relation in the extended relationshipof said members, a quantity of fluid contained within said inner andouter members including within the annular volume of said annularclearance space defined between said second bearing element and saidsealing member with the parts in the extended relationship thereof, ametering rod rigidly afiixed to one end of said outer member within thesame, a piston wall formed at the inner end of said inner member andincluding an aperture centrally therein, said piston wall definingvariable volume fluid chambers, and an annular orifice member includingan annular wall mounted within said aperture and sized for limitedradial shifting therewithin and a pair of radially extending integralflanges embracing said piston wall with clearance whereby said orificemember is retained on the latter yet is radially shiftable relative:thereto to accommodate axial misalignment between said rod and saidaperture during telescoping of said members.

1. An energy absorbing mounting unit for impact bumper bars ofautomotive vehicles comprising inner and outer tubular members the innerof which is adapted for attachment to a said bar and the outer of whichis adapted for attachment to the vehicle structural frame, said innermember being slidably received within said outer member with an annularclearance space between the walls thereof and for telescoping movementbetween a selected extended relationship and any of a plurality oftelescoped relationships, bearing means between said members permittingrelatively free telescoping movement of said members under impactsapplied to said bumper bar and including a first bearing element locatedadjacent the terminal open end portion of said outer member and a secondbearing element spaced from said first element within said outer memberlongitudinally a distance substantially equaling the length of saidinner member enclosed by said outer member in said extended relationshipof said members, said second bearing element defining fluid passagemeans permitting communication of fluid either side thereof, axiallyaligning load supporting taper surfaces on said members including afirst generally taper surface on said terminal end portion of said outermember and a complementary taper surface on said inner member engageablein the extended relationship of said members, an annular sealing memberdisposed on said inner member immediately closely adjacent therespective said taper surface thereon and thereby uniformly sealinglyengageable about its periphery between said members in an axiallyaligned relation with said taper surfaces engaged in the extendedrelationship of said members, and a quantity of fluid sealedly containedwithin said inner and outer members by said sealing member includingwithin the annular volume of said annular clearance space definedbetween said second bearing element and said sealing member with theparts in the extended relationship thereof.
 2. An energy absorbingmounting unit for impact bumper bars of automotive vehicles comprising,inner and outer tubular members the inner of which is adapted forattachment to said bar and the outer of which is adapted for attachmentto the vehicle structural frame, said inner member being slidablyreceived within said outer member with an annular clearance spacebetween the walls thereof and for telescoping movement between aselected extended relationship and any of a plurality of telescopedrelationships, bearing means between said members permitting relativelyfree telescoping movement of said members under impacts applied to saidbumper bar and including a first bearing element mounted on said innermember at a location engageable with the terminal end portion of saidouter member with the members in extended relation and a second bearingelement mounted on said inner member at a location spaced from saidfirst element longitudinally a distance substantially equaling thelength of said inner member enclosed by said outer member in saidextended relationship of said members, said second bearing elementdefining fluid passage means permitting communication of fluid eitherside thereof, stabilizing means on said members including a firstgenerally frusto-conical crimp surface at the margin of said outerterminal end portion of said outer member and a complementaryfrusto-conical surface on said inner member engageable in the extendedrelationship of said members to axially align said members and providefirm lateral load bearing support between said members in said extendedrelationship thereof, an annular sealing member disposed on said innermember immediately closely adjacent said complementary frusto-conicalsurface and thereby uniformly sealingly engageable about its peripherybetween said members in a centered relation in the extended relationshipof said members, and a quantity of fluid contained within said inner andouter members including within the annular volume of said annularclearance space defined between said second bearing element and saidsealing member with the parts in the extended relationship thereof. 3.An energy absorbing mounting unit for impact bumper bars of automotivevehicles comprising, inner and outer tubular members, one of saidmembers being adapted for attachment to the vehicle and the otherthereof for attachment to a bumper bar, said inner member beingrelatively freely slidably received within said outer member forrelative telescoping motion under impact forces applied to the bumperbar from a normal extended relationship to any of a plurality oftelescoped relationships, means biasing said members to said normalextended relationship thereof, means defining a pair of variable volumefluid chambers within said members, fluid within said chambers, ametering rod rigidly affixed to one of said members, a piston wall onthe other of said members and an aperture in said piston wallcommunicating said chambers and having projecting therethrough an endportion of said rod, and an annular orifice member including an annularwall mounted within said aperture of said piston wall to extend in adirection axially of said members past both sides of said piston walland sized for limited radial shifting movement within said aperture,said annular wall receiving said end portion of said rod, said orificemember further including a pair of radially extending flanges integralwith said annular wall and embracing said piston wall with clearancewhereby said orifice member is retained on said piston wall yet isradially shiftable to accommodate axial misalignment between said rodand said aperture during telescoping movement of said members betweensaid normal extended relationship and a maximum telescoped relationship.4. The mounting unit recited in claim 3 wherein said metering rod isshaped generally cylindrical along its length and includes at least onevarying depth flat thereon interrupting the cylindricity thereof, thecylindrical contour of said metering rod being engaged with acylindrical inner surface of said orifice member annular wall forguiding the latter radially in said aperture.
 5. An energy absorbingmounting unit for impact bumper bars of automotive vehicles comprising,inner and outer tubular members the inner of which is adapted forattachment to said bar and the outer of which is adapted for attachmentto the vehicle structural frame, said inner member being slidablyreceived within said outer member with an annular clearance spacebetween the walls thereof and for telescoping movement between aselected extended relationship and any of a plurality of telescopedrelationships, bearing means between said members pErmitting relativelyfree telescoping movement of said members under impacts applied to saidbumper bar and including a first bearing element mounted on said innermember at a location engageable with the terminal end portion of saidouter member with the members in extended relation and a second bearingelement mounted on said inner member at a location spaced from saidfirst element longitudinally a distance substantially equaling thelength of said inner member enclosed by said outer member in saidextended relationship of said members, said second bearing elementdefining fluid passage means permitting communication of fluid eitherside thereof, stabilizing means on said members including a firstgenerally frusto-conical crimp surface at the margin of said outerterminal end portion of said outer member and complementaryfrusto-conical surface on said inner member engageable in the extendedrelationship of said members to axially align said members and providefirm lateral load bearing support between said members in said extendedrelationship thereof, an annular sealing member disposed on said innermember immediately closely adjacent said complementary frusto-conicalsurface and thereby uniformly sealingly engageable about its peripherybetween said members in a centered relation in the extended relationshipof said members, a quantity of fluid contained within said inner andouter members including within the annular volume of said annularclearance space defined between said second bearing element and saidsealing member with the parts in the extended relationship thereof, ametering rod rigidly affixed to one end of said outer member within thesame, a piston wall formed at the inner end of said inner member andincluding an aperture centrally therein, said piston wall definingvariable volume fluid chambers, and an annular orifice member includingan annular wall mounted within said aperture and sized for limitedradial shifting therewithin and a pair of radially extending integralflanges embracing said piston wall with clearance whereby said orificemember is retained on the latter yet is radially shiftable relativethereto to accommodate axial misalignment between said rod and saidaperture during telescoping of said members.